1. Field of the Invention
The present invention relates to a transmitter/receiver for use in multichannel time division duplexing (TDD) system and, more particularly, to a transmitter/receiver which provides isolation between transmission channels during a transmission mode of operation and reception channels during a reception mode of operation.
2. Description of the Related Art
Referring to FIG. 1, a conventional transmitter/receiver (employed in a multichannel time division duplexing (TDD) system) having one port (i.e., a physical channel) for transmitting and receiving data is shown. The conventional transmitter/receiver includes an antenna 2, a first circulator 4 and a second circulator 8, a low noise amplifier (LNA) 6, a Wilkinson combiner/divider 10, a first switch 12-1 and a second switch 12-2, a first power amplifier (PA) 14-1 and a second power amplifier (PA) 14-2, a third switch 16-1 and a fourth switch 16-2, a first transceiver 18-1 and a second transceiver 18-2, and a switching control circuit 20. The first and second power amplifiers 14-1 and 14-2, respectively, are enabled in response to a transmission enable signal generated from the switching control circuit 20 (indicated by dotted line S1). The low noise amplifier 6 is enabled in response to a reception enable signal generated from the switching control circuit 20 (indicated by dotted line S2).
In a transmission mode of operation, transmission signals generated from the first transceiver 18-1 and the second transceiver 18-2 are transferred to the Wilkinson combiner/divider 10 through a first and a second transmission channel, respectively. The first transmission channel comprises the first switch 12-1, the third switch 16-1, and the first power amplifier 14-1. The second transmission channel comprises the second switch 12-2, the fourth switch 16-2 and the second power amplifier 14-2. The Wilkinson combiner/divider 10 combines the transmission signals received from the first and second transmission channels and transfers the combined transmission signals to the antenna 2 through the first circulator 4 and the second circulator 8. In the transmission mode, the low noise amplifier 6 is disabled so as to prevent the transmission signal output of the first circulator 4 from being transferred back to the second circulator 8 through the low noise amplifier 6.
Next, in a reception mode of operation, a signal received through the antenna 2 is transferred to the low noise amplifier 6 which is enabled by the reception enable signal (S2) generated from the switching control circuit 20. The low noise amplifier 6 then amplifies the received signal and sends the amplified signal to the Wilkinson combiner/divider 10 via the second circulator 8. The Wilkinson combiner/divider 10 divides the amplified signal and sends the divided signals to the first transceiver 18-1 and the second transceiver 18-2 through a first and a second reception channel, respectively. The first reception channel comprises the first switch 12-1 and the third switch 16-1. The second reception channel comprises the second switch 12-2 and the fourth switch 16-2. In the reception mode, the first power amplifier 14-1 and the second power amplifier 14-2 are disabled so as to prevent the output signals from the third switch 16-1 and the fourth switch 16-2 from being transferred back to the first switch 12-1 and the second switch 12-2, respectively, through the power amplifiers 14-1. and 14-2.
There are several problems with the conventional transmitter/receiver described above. For example, the device includes a significant amount of switches, which increases the size as well as the complexity of the system. Further, since the switches (12-1, 12-2, 16-1, and 16-2) are active elements, they have the poor intermodulation distortion (IMD) characteristics (as compared to the first and second circulators 4 and 8 which are passive elements). Moreover, since the conventional device includes the single Wilkinson combiner/divider 10, transmission signals may be fed back through the reception channels via the Wilkinson combiner/divider 10.